1. Field of the Invention
The present invention relates to a transformer as a data transferring unit arranged between a main unit and a line unit in a facsimile in order to prevent power source noise generated at a power supplier to flow into the line unit and preventing noise entering from a public switched telephone network to the line unit, and a communication interface unit of a facsimile using the same.
2. Description of the Related Art
A facsimile is a device for transmitting a document to other facsimile connected through a public switched telephone network (PSTN). The facsimile scans the document to generate image data of the document and transfers the image data to other facsimile. Also, the facsimile receives the image data from other facsimile and prints the image data on a plain paper.
Generally, the facsimile is connected to the PSTN and transmits the image data by telephoning the other facsimile.
FIG. 1 is a block diagram illustrating a conventional facsimile.
By referring to FIG. 1, the conventional facsimile 100 includes a main unit 110, a first condenser C1 131, a second condenser C2 133 and a line unit 150.
The main unit 110 controls general operations of the facsimile 100 for scanning a document to generate image data and processing the image data to be transmitted to other facsimile (not shown). The main unit 100 includes a central processing unit 111, a MODEM 113 and a line interface 115.
The central processing unit 111 generates image data by scanning the document and transfers the image data to the line unit 150 through the MODEM 113 and the line interface 115.
The line unit 150 is directly connected to the PSTN where the facsimile is connected. The line unit 150 transmits the image data by telephoning to other facsimile and receives the image data from other facsimile by accepting an incoming call from the other facsimile.
The line unit 150 includes a data access arrangement (DAA) block (not shown). The DAA block receives digital data of the image data from the main unit 110 and converts the received digital data to analog data. Also, the DAA block transmits the analog data to other facsimile by telephoning the other facsimile. Recently, an integrated circuit is commonly used as the DAA block. Hereinafter, the DAA block is called a silicon DAA.
Meanwhile, a reference electric potential of the main unit 110 and a reference electric potential of the line unit 150 should be different. Therefore, the main unit 110 and the line unit 150 are implemented to have separated circuit boards or to separate a ground from the circuit board. By using separated circuit boards or separating the ground from the circuit board, it protects the facsimile 100 and a user of the facsimile 100 from a high voltage noise flowing into the main unit 110 when the high voltage noise enters from the PSTN to the line unit 150.
Therefore, the main unit 110 and the line unit 150 are designed to be separated and they are connected by the first condenser C1 131 and the second condenser C2 133. Also, the first condenser C1 131 and the second condenser C2 133 eliminate low frequency noise transferred from the line unit 150.
However, when a noise such as an electrical fast transient EFT is applied to an electric power supplied to the main unit 110, the noise is transferred to the line unit 150 through the first condenser C1 131 and the second condenser C2 133. Thus, the image data may be distorted by the noise. The distortion of image data becomes more serious when the silicon DAA is used.